Rotors of steam turbines are exposed to high stresses caused by centrifugal forces and temperature differences. The former mainly restrict the diameter of the rotor which can be installed, while the latter mainly reduce the service life as a result of LCF (Low Cycle Fatigue) stresses.
Hitherto, rotors have been produced primarily from steel alloys, in some cases using large cavities, as are formed in the case of rings of rotors welded together (cf. for example WO-A1-2004/101209).
On the other hand, it is known to foam metals and in this way to produce porous metal structures. Extensive tests have been carried out using aluminum foams (cf. for example U.S. Pat. No. B1-6,840,301). It is also known that foaming is in principle possible for all metals, i.e. including steels (cf. for example U.S. Pat. No. 6,263,953). The metal foams in this case have a continuous surface. The foam structure is therefore not visible from the outside.